With Flu Season Coming,
Don’t Forget…Exercise?
New study shows direct,
beneficial effect of short-term moderate exercise on susceptibility to upper
respiratory tract infection
November 10, 2003 - (Bethesda, MD) – With
winter around the corner, Americans are lining up for flu shots, stocking up
on cough and cold medicines, and taking inventory of what antibiotics they
may again need. Despite expansive planning, few remember two low-tech
staples that can be easily and affordably added to their first line defenses
against the illnesses of the season: exercise and oat fiber β-glucan.
Individually, moderate exercise and the soluble oat
fiber β-glucan increase immune function and decrease the risk of infection.
However, no information exists about the possible benefits of combining the
two. A new study, using an animal model of induced respiratory infection,
looks at the direct effects of a short period of moderate exercise training
and consumption of soluble oat fiber β-glucan on the illness (morbidity) and
death (mortality) following exposure to an upper respiratory tract infection
(URTI). The study concludes that that moderate exercise alone is associated
with a significant reduction in risk.
Background: How It Works
Exercise - It was thought that moderate exercise
may enhance resistance to infection by activating the release of
immunostimulatory factors (such as growth hormones, prolactin and
cytokines), which in turn activate various immune cell populations.
Exercise bouts of moderate duration (<60 min) and lower intensity (<60 %Vo2
max) have been associated with enhanced activity of immune parameters,
including macrophage chemotaxis, oxidative metabolism and phagocytic
activities, as well as increased natural killer (NK) cell activity. These
cells may constitute an important part of a first-line defense against URTI
by nature of their phagocytic, cytotoxic and intracellular killing
capacities.
Oat Fiber β-Glucan - β-Glucans (polysaccharides
derived from the cell wall of yeast, fungi, algae and oats) have been shown
to enhance the activities of both the non-specific and specific immune
system but have received little attention in the field of exercise
immunology. β-Glucan exerts its effects through the direct stimulation of
macrophage, neutrophil and NK cells via β-glucan specific receptor sites.
When bound, β-glucan activates key cells, which set off a cascade of immune
defenses that protect the organism from various viral, bacterial and fungal
challenges. The exact mechanisms are at least partially dependent on the
route of administration; protection following oral administration results
primarily from certain effects of ingestion, for example.
A New Study
The authors of a new study, entitled “Effects of
Moderate Exercise and Oat β-glucan on Innate Immune Function and
Susceptibility to Respiratory Infection,” are J.M. Davis, E.A. Murphy, A.S.
Brown, M.D. Carmichael, A. Ghaffar and E.P. Mayer, all of the University of
South Carolina, Columbia, SC. Their findings are published in the online
edition of “Articles in Press” for the American Journal of Physiology –
Regulatory, Integrative and Comparative Physiology. The journal is one
of 14 scientific periodicals published each month by the American
Physiological Society (APS).
Methodology
The researchers used the following protocol:
Mice: Male CD-1 mice, four weeks of age, were
acclimated at the research facility 3+ days prior to experimentation. They
were maintained on a 12:12-hour light-dark cycle in a low stress environment
and given food (chow) and water (oat β-glucan dissolved in water) ad
libitum. Separate groups of mice were used for each dependent variable:
in vivo susceptibility to infection (n=24 per group), macrophage anti-viral
resistance (n=18 per group), and natural killer (NK) cell cytotoxicity (n=12
per group).
Nutrient Treatment: Mice were randomly assigned
to one of four groups: exercise water (Ex-H20), exercise oat β-glucan
(Ex-OβG), control water (Con-H20), or control oat β-glucan (Con-OβG).
Ex-H20 and Con-H20 received tap water for the ten days
prior to inoculation/death, while Ex-OβG and Con- OβG mice were fed a
solution of oat β-glucan dissolved in the drinking water for the 10 days
prior to inoculation/death. Oat β-glucan was not fed to the animals during
the 21 days following inoculation.
Treadmill Acclimation and Exercise Protocol: On
the second day of oat β-glucan/water treatment, exercise mice (Ex-H20
and Ex-OβG) were acclimated to a treadmill for 20 min/day. The exercise
protocol consisted of a one-hour bout of treadmill running for six
consecutive days. Mice in the control groups (Con-H20 and Con-OβG)
remained in their cages in the treadmill room during the bouts.
Intranasal Inoculation of and Infection with HSV-1:
Intranasal inoculation of Herpes simplex virus type 1 (HSV-1) VR strain
was administered. This strain in the mouse is an established experimental
model of respiratory infection; this route was chosen to mimic the typical
route of entry for viral infection. On the day of the experiment mice (n=24
per group) were exposed to either control treatment or exercise for one hour
and immediately returned to their cages. Fifteen minutes later they were
anesthetized and inoculated intranasally with 50 μL of HSV-1 VR strain.
Following infection, the mice were returned to their respective cages and
monitored twice daily for 21 days for signs of morbidity/mortality.
Peritoneal Macrophage Antiviral Resistance: On
the day of experiment, mice (n=12 per group) were exposed to either control
or exercise treatment. Immediately following exercise or rest they were
euthanized. Peritoneal macrophages were collected, prepared and infected
with HSV-1. The virus was allowed to absorb for 90 minutes and, 72 hours
after infection, anti-viral resistance was quantified.
NK Flow Cytometric Assay: On the day of
experiment, mice (n=12 per group) were either exposed to control or exercise
treatment and euthanized 30 min/post-treatment. Spleens were removed and
weighed, and blood cells were immediately lysed. Two parameter flow
histograms were conducted.
TNF-α and Statistical Analysis: Blood was
collected and plasma assayed for TNF- α. Statistical analyses were
performed for differences in morbidity and mortality across the 21-day
post-infection period. Differences in NK cell activity, macrophage
anti-viral resistance, TNF- α, weight gain and fluid consumption were
compared using a two-way analysis of variance.
Results
Highlights of the findings include:
-
Morbidity: There were differences in morbidity across
the groups over the 21-day post-infection period. Intranasal
administration of HSV-1 following short-term moderate exercise training
resulted in a decrease in morbidity as compared with resting controls.
Exercise mice (Ex-H20) experienced only a 13% incidence in
morbidity while 58% percent of control mice (Con-H20) exhibited
such symptoms. Consumption of oat β-glucan for ten days prior to
inoculation did not further decrease the symptoms of morbidity as there
was no real difference between the Ex-H20 group (13%) and the
Ex-OβG group (21%).
-
Mortality: Similar effects were found for mortality over the 21-day
post-infection period among the four groups. Intranasal administration of
HSV-1 following six days of moderate exercise resulted in a decrease in
mortality compared to control mice. Ex-H20 mice showed a
mortality rate of 8% over the 21-day period compared with a 46% rate among
the Con-H20 mice. Consumption of oat β-glucan for ten days
prior to inoculation did not further decrease mortality in the exercise
animals; there were no significant differences between Ex-H20
and Ex-OβG mice. However, oat β-glucan administration did show a trend
toward decreasing mortality in the control mice, prolonging the survival
time of resting animals. Con-H20 mice showed a mortality rate
of 46% while Con-OβG mice experienced a mortality rate of only 33%.
-
Peritoneal Macrophage Anti-Viral Resistance: The
intrinsic anti-viral resistance in mice exercised moderately for six days
(Ex-H20) was significantly greater than in control mice (Con-H20).
Oat β-glucan consumption for ten consecutive days did not further enhance
the benefits of exercise. However, resting mice consuming oat β-glucan
dissolved in the drinking water for ten days prior to death (Con-OβG) had
a significantly greater macrophage anti-viral resistance than did resting
mice drinking water (Con-H20).
-
NK Cytotoxicity, TNF-a: Six days of moderate exercise
was associated with a very small increase in splenic NK cytotoxicity at
effector:target ratios of 5:1 and 1:1, but not at 20:1 and 80:1, compared
with non-exercised controls. Oat β-glucan consumption did not result in
any change in NK cytotoxicity. The presence of TNF-α was not detectible
above 3 pg in any of the groups following moderate exercise or oat β-glucan
treatment. Therefore, moderate exercise or oat β-glucan consumption was
not associated with an elevation of this cytokine.
Conclusions
These results support the hypothesis that moderate
exercise training can decrease susceptibility to induced respiratory
infection in mice. These data also provide evidence of a role for
macrophages and NK cells as mediators of this benefit on host protection.
While there were no added benefits of oat β-glucan in this experiment, it
deserves further research to evaluate the positive trends observed in both
the immune function and infection rates.
-end-
Source: Online edition of “Articles in Press” for the Journal
of Applied Physiology.
The American Physiological Society (APS)
was founded in 1887 to foster basic and applied science, much of it relating
to human health. The Bethesda, MD-based Society has more than 10,000 members
and publishes 3,800 articles in its 14 peer-reviewed journals every year.
***
Editor’s Note: A copy of the research article is
available in pdf format to the press. Members of the press are invited to
obtain a pdf copy of the study and to interview members of the research
team. To do so, please contact Donna Krupa at 703.527.7357 (direct dial),
703.967.2751 (cell) or djkrupa1@aol.com.
